Abnormality diagnosing device for internal combustion engine and abnormality diagnosing method therefor

ABSTRACT

A temperature of a catalyst disposed in an exhaust system is raised to a target bed temperature by supplying an unburned fuel component to the catalyst. A learned value is updated based upon a catalyst bed temperature under a temperature increase control and the target bed temperature so that the learned value corresponds to a difference between the respective temperatures. Whether the learned value is out of a proper range or not is determined whenever the learned value is updated. Abnormality is determined when determination that the learned value is out of the proper range is made over several successive updates of the learned value.

INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2006-168847 filed onJun. 19, 2006 including the specification, drawings and abstract isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an abnormality diagnosing device for aninternal combustion engine and an abnormality diagnosing methodtherefor.

2. Description of the Related Art

Conventionally, as an exhaust gas purification system of an internalcombustion engine such as, for example, a diesel engine for a vehicle, asystem including a particulate matter (PM) filter and a catalyticconverter disposed in an exhaust system is known. The PM filter traps PMwhose major component is soot. The catalytic converter includes astorage reduction type NOx catalyst for purifying exhaust gas, i.e.,nitrogen oxides (NOx). In such an exhaust gas purification system, atemperature increase control is executed to raise a temperature of thecatalyst to a target bed temperature by supplying unburned fuelcomponents to the catalyst to recover an exhaust gas purificationcapacity.

For example, accumulation of the particulate matter clogs the PM filterand the catalytic converter. However, the filter may be regenerated byburning (oxidizing) the particulate matter, which eliminates theclogging. The temperature increase control is executed to regenerate thefilter. In the temperature increase control, the unburned fuelcomponents are supplied to the catalyst, and components such as, forexample, a hydro carbon (HC) and a carbon monoxide (CO) are oxidized inthe exhaust gas or on the catalyst. The heat generated by theoxidization raises the bed temperature of the catalyst to a target bedtemperature. Because the catalyst bed temperature is increased, the PMfilter and the catalytic converter are placed under the high temperaturecircumstances. The accumulating particulate matter is thus removed. Thecapacity of the PM filter for the particulate matters is recovered,accordingly.

Meanwhile, occasionally, the catalyst bed temperature does not reach thetarget bed temperature even though the unburned fuel components aresupplied to the catalyst to raise the temperature to the target bedtemperature. For example, if a fuel supply system through which theunburned fuel components are supplied to the catalyst is clogged, theamount of the unburned fuel components supplied to the catalyst may beless than the amount required. The deficiency in the amount suppliedcauses the actual catalyst bed temperature to deviate from the targetbed temperature.

In order to determine whether such abnormality occurs or not.JP-A-2003-172185 describes in paragraphs [0065] through [0068] thefollowing abnormality diagnosis. That is, during the temperatureincrease control to regenerate the filter, a learned value is updatedbased upon the catalyst bed temperature and the target bed temperatureso that the learned value corresponds to the difference between therespective temperatures. The updated learned value is reflected to thesupply amount of the unburned fuel components to the catalyst. Also,presence of the abnormality is determined by determining whether thelearned value is within a proper range or not. On this occasion, if theabnormality described above occurs, the learned value is outside of theproper range. The abnormality thus is determined based upon thedetermination that the learned value is outside of the proper range.

In the meantime, regarding the abnormality such that the catalyst bedtemperature does not reach the target bed temperature even though theunburned fuel components are supplied to the exhaust system to raise thecatalyst bed temperature to the target bed temperature, this abnormalitydoes not necessarily permanently occur but can temporarily occur. Thelearned value that is updated to correspond to the difference betweenthe catalyst bed temperature and the target bed temperature is out ofthe preset proper range as long as the abnormality continues.

As one of situations in which such a temporary abnormality occurs, asituation can be exemplified such that a supplemental fuel valve is usedto supply supplemental fuel to the exhaust system for supplying theunburned fuel components to the catalyst, and, due to use of poorquality fuel, deposits adhere to the periphery of a nozzle of thesupplemental fuel valve. The adhesion of the deposits to the nozzleperiphery of the supplemental fuel valve decreases the amount of theunburned fuel components supplied to the catalyst. As a result, despiteof the attempt to raise the catalyst bed temperature to the target bedtemperature by supplying the supplemental fuel through the supplementalfuel valve, the abnormality occurs such that the catalyst bedtemperature does not reach the target bed temperature. However, eventhough the deposits adhere to the nozzle periphery of the supplementalfuel valve due to the use of the poor quality fuel, such deposits arehighly likely to depart from the nozzle periphery while the supplementalfuel being supplied. Therefore, the occurrence of the abnormalityaccompanying the adhesion of the deposits is temporary.

The abnormality diagnosis described in JP-A-2003-172185 may incorrectlydetermine that an abnormality is present. This is because the temporaryabnormality affects the catalyst bed temperature, and, when the learnedvalue that is updated to correspond to the difference between thecatalyst bed temperature and the target bed temperature is outside ofthe preset proper range, the abnormality is immediately determined basedupon the determination that the learned value is out of the properrange. That is, if the abnormality disappears after the abnormality isdetermined, the determination of the abnormality is incorrect.

SUMMARY OF THE INVENTION

The invention provides an abnormality diagnosing device for an internalcombustion engine and an abnormality diagnosing method therefor thatavoids incorrect abnormality determination when a temporary abnormalityoccurs.

A first aspect of this invention relates to an abnormality diagnosingdevice for an internal combustion engine in which a temperature increasecontrol for increasing a temperature of a catalyst disposed in anexhaust system to a target bed temperature is executed by supplying anunburned fuel component to the catalyst, updating of a learned value isexecuted based upon a catalyst bed temperature under the temperatureincrease control and the target bed temperature so that the learnedvalue corresponds to a difference between the respective temperatures,and an abnormality is determined based upon the learned value when thelearned value is updated. The abnormality diagnosing device includeslearned value determining means for determining whether the learnedvalue is outside of a proper range or not when the learned value isupdated, and determines that an abnormality is present only when thelearned value falls outside of the proper range over several successiveupdates of the learned value.

The abnormality such that the catalyst bed temperature does not reachthe target bed temperature even though the unburned fuel components aresupplied to the exhaust system to keep the catalyst bed temperature onthe target bed temperature does not necessarily permanently occur butcan temporarily occur. Even though the difference between the catalystbed temperature and the target bed temperature is temporary, the learnedvalue is updated to correspond to the difference, and the learned valuemay fall outside of the proper range. When this occurs, if theabnormality is immediately determined when the learned value fallsoutside of the proper range, the determination of the abnormality may beincorrect when the temporary abnormality disappears afterwards. However,according to the construction described above, even though the learnedvalue falls outside of the proper range, the abnormality is notdetermined unless the learned value falls outside of the proper rangeover several successive updates of the learned value. Therefore, theabnormality is not incorrectly determined when the catalyst bedtemperature and the target bed temperature are temporarily inconsistentwith each other.

In this aspect, the internal combustion engine may have a supplementalfuel valve for supplying supplemental fuel upstream of the catalyst inthe exhaust system.

According to the above construction, the supplemental fuel valvesupplies supplemental fuel to supply the unburned fuel components to thecatalyst disposed in the exhaust system. In this connection, if poorquality fuel is used, deposits are likely to adhere to the periphery ofthe nozzle of the supplemental fuel valve. The adhesion of the depositsreduces the amount of the fuel supplied through the supplemental fuelvalve which causes the catalyst bed temperature to be lower than thetarget bed temperature. However, the deposits adhering to the nozzleperiphery of the supplemental fuel valve is highly likely to come offfrom the nozzle periphery while the supplemental fuel being supplied.The abnormality such that the catalyst bed temperature varies from thetarget bed temperature thus can be temporary. Therefore, it isdetermined that an abnormality is not present based upon such atemporary abnormality.

In the aspect, the exhaust system of the internal combustion engine mayhave a filter for trapping particulate matter. The temperature increasecontrol for increasing the temperature of the catalyst to the target bedtemperature may be executed by supplying the unburned fuel component tothe catalyst when to burn the particulate matter to regenerate thefilter. Thus, reducing the amount of particulate matter trapped in thefilter is to less than a prescribed amount.

According to the above construction, the filter regeneration isregularly made maintain the amount of particulate matter accumulating inthe catalyst to less than a prescribed amount. When thetemperature-increase control for the filter regeneration is executed,the abnormality may be simultaneously determined. Chances for theabnormality determination are not reduced, accordingly.

In the first aspect, the abnormality diagnosing device may have countingmeans for increasing a count value when the learned value determiningsection determines that the learned value has fallen outside of theproper range and resets the count value to an initial value, forexample, “0” when the learned value determining section determines thatthe learned value is in the proper range. The abnormality determiningmeans determines that an abnormality is present when the count valuebecomes a determination value that is equal to or greater than a valuethat is incremented at least twice from the initial value, e.g., aninteger such as “2”. The counting means can reset the count value to theinitial value when the filter regeneration is completed.

If the abnormality that the catalyst bed temperature does not reach thetarget bed temperature temporarily occurs during the temperatureincrease control for the filter regeneration, the updated learned valuefall outside of the proper range and the counting means increases thecount value. If, however, the temporary abnormality does not affect thefilter regeneration so much, the filter regeneration may be completedbecause the accumulation amount of the particulate matter on thecatalyst decreases to be less than the prescribed amount before thecount value exceeds the abnormality threshold value. On this occasion,if the count value is maintained above “0,” the count value reaches orexceeds the determination value soon once the learned value varies to beout of the proper range because the temporary abnormality again occursduring the subsequent temperature increase control for the filterregeneration. Consequently, the abnormality can be incorrectlydetermined. According to the above construction, however, the countvalue is reset to “0” whenever the filter regeneration is completed. Theincorrect abnormality determination described above thus can be avoided.

In the first aspect, the abnormality diagnosing device can have countingmeans for increasing a count value when the learned value determiningmeans determine that the learned value has fallen outside of the properrange and resets the count value to an initial value when the learnedvalue determining means determine that the learned value is in theproper range. The learned value is updated when the catalyst bed stablymaintains a catalyst bed temperature that is equal to or higher than thetemperature at which the particulate matter burns. The abnormalitydetermining means determine that an abnormality is present when thecount value given by the counting means becomes a determination valuethat is equal to or greater than a value that is incremented at leasttwice from the initial value, e.g., an integer such as “2”. Theabnormality determining means may also determine that an abnormality ispresent, regardless of the count value, if the filter regeneration isnot completed after the elapsed time from when the filter regenerationstarts reaches or exceeds a permissible time period.

When the abnormality occurs such that the catalyst bed temperature doesnot reach the target bed temperature during the temperature increasecontrol for the filter regeneration, the learned value is not updatedunless the catalyst bed temperature stably maintains a catalyst bedtemperature that is equal to or higher than the temperature at which theparticulate matter accumulating in the catalyst burns even though theupdated learned value may fall outside of the proper range. Under thecondition, despite of occurrence of the abnormality, the filterregeneration continues with the count value remaining less than thedetermination value, i.e., without the abnormality being determined. Thefilter regeneration is highly likely to stay uncompleted under thecondition because the particulate matters accumulating in the catalystare hardly burned. According to the above construction, however, if thefilter regeneration is not completed even though the time elapsing fromthe start moment of the filter regeneration reaches or exceeds thepermissible time period, the abnormality is determined whether or notthe count value is still less than the abnormality threshold value.Thus, the abnormality can be determined whenever the abnormalityactually occurs.

In the aspect, the abnormality determining means can determine that anabnormality is present when the learned value determining meansdetermine that the learned value varies to be larger than the properrange over several successive updates of the learned value.

In the aspect, the unburned fuel component can be supplied to thecatalyst by an auxiliary injection made in an exhaust stroke or anexpansion stroke after fuel is injected for combustion in a combustionchamber from a fuel injector.

A second aspect of this invention relates to an abnormality diagnosingmethod for an internal combustion engine in which a temperature increasecontrol for increasing a temperature of a catalyst disposed in anexhaust system to a target bed temperature is executed by supplying anunburned fuel component to the catalyst, updating a learned value isexecuted based upon a catalyst bed temperature under the temperatureincrease control and the target bed temperature so that the learnedvalue corresponds to a difference between the respective temperatures,and abnormality is determined based upon the learned value when thelearned value is updated. In this method, it is determined whether thelearned value falls outside of a proper range every time the learnedvalue is updated. Also, an abnormality is determined to be present whenit is determined that the learned value falls outside of the properrange over several successive updates of the learned value.

In this aspect, preferably, the exhaust system of the internalcombustion engine can have a filter for trapping particulate matter. Thetemperature increase control for increasing the temperature of thecatalyst to the target bed temperature can be executed by supplying theunburned fuel component to the catalyst when a filter regeneration ismade to burn the particulate matters so that an accumulation amount ofthe particulate matter trapped by the filter is to be less than a presetamount.

In the aspect, a count value can be increased when the learned value isdetermined to fall outside of the proper range. The count value is resetto an initial value when the learned value is determined to be in theproper range. An abnormality is determined to be present when the countvalue is greater than a determination value that is equal to or greaterthan a value that is incremented at least twice from the initial value.The count value can be reset to the initial value when the filterregeneration is completed.

In the aspect, a count value can be increased when the learned value isdetermined to be outside of the proper range. The count value can bereset to an initial value when the learned value is determined to be inthe proper range. The learned value can be updated when the catalyst bedtemperature is stably maintained at a temperature that is equal to orabove the temperature at which the particulate matter burns. Theabnormality can be determined to be present when the count value isequal to or greater than a determination value that is equal to orgreater than a value that is incremented at least twice from the initialvalue. The abnormality is determined to be present regardless of thecount value if the filter regeneration is not completed after a timeperiod has elapsed from a start moment of the filter regenerationreaches or exceeds a permissible time period.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and further objects, features and advantages of theinvention will become apparent from the following description of exampleembodiments with reference to the accompanying drawings, wherein likenumerals are used to represent like elements and wherein:

FIG. 1 is a schematic view showing an overall structure of an internalcombustion engine to which an abnormality diagnosing device of thisembodiment is applied.

FIGS. 2A through 2D are time charts showing a change of supply pulsesfor driving a supplemental fuel valve during a temperature increasecontrol for filter regeneration, changes of a catalyst bed temperature Tand a catalyst inlet port exhaust temperature Tb, transitions ofintegration values ΣQr, ΣQ, and a set mode of an supplement permissionflag F1, respectively.

FIG. 3 is a flowchart showing control processes for fuel supplementationmade by the supplemental fuel valve during the temperature increasecontrol.

FIG. 4 is another flowchart showing successive control processes for thefuel supplementation made by the supplemental fuel valve during thetemperature increase control;

FIG. 5 is a time chart showing a condition under which a stationarydifference appears between the catalyst bed temperature (catalyst bedtemperature average value Tave) and a target bed temperature Tt.

FIG. 6 is a time chart showing the integration values ΣQr, ΣQ in asituation that a learned value K is not reflected.

FIG. 7 is a time chart showing the integration values ΣQr, ΣQ in asituation that a learned value K is reflected.

FIG. 8A is a time chart showing transitions of the catalyst bedtemperature average value Tave and the target bed temperature Ttprovided when a stationary difference therebetween disappears, and FIG.8B is a time chart showing a transition manner of the learned value Kunder the same condition.

FIG. 9 is a flowchart showing a learned value updating routine forstoring the learned value K into a nonvolatile RAM.

FIG. 10 is a time chart showing a transition of the learned value K madeeach time the learned value K is updated when a temporary abnormalityoccurs.

FIGS. 11A and 11B are time charts showing the transition of the learnedvalue K made each time the learned value K is updated and a transitionof a count value of a counter C, respectively.

FIG. 12 is a flowchart showing abnormality diagnosing processes of thisembodiment.

FIGS. 13A and 13B are time charts showing the transition of the learnedvalue K made each time the learned value K is updated and a transitionof a count value of a counter C, respectively.

FIGS. 14A through 14C are time charts showing the transition of thelearned value K made each time the learned value K is updated, thetransition of the count value of the counter C, and a change mode of anabnormality flag F2, respectively.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to FIGS. 1 through 14, one embodiment in which thepresent invention is embodied will be described below. FIG. 1 shows thestructure of an internal combustion engine 10 equipped with anabnormality diagnosing device of the embodiment of the invention. Theengine 10 is a diesel engine for an automobile and has a common-railtype fuel injection device.

An intake passage 12 forms part of the intake system of the engine 10.An exhaust passage 14 forms part of the exhaust system of the engine 10.The intake and exhaust passages 12 and 14 are individually connected tothe combustion chambers 13 of respective cylinders of the engine 10. Anairflow meter 16 and an intake throttle valve 19 are placed in theintake passage 12. A catalytic converter 25 for NOx, a PM filter 26 anda catalytic converter 27 for oxidation are placed in the exhaust passage14 in this order from the upstream portion of the exhaust passage 14.

The catalytic converter 25 for NOx contains a storage reduction type NOxcatalyst. The NOx catalyst absorbs and stores NOx in exhaust gas whenthe oxygen concentration of the exhaust gases is high, and dischargesthe NOx which has been stored when the oxygen concentration of theexhaust gas is low. Also, the NOx catalyst reduces the discharged NOx topurify the exhaust gas if sufficient unburned fuel components, which actas reducing agents, are present around the catalyst when the NOx isdischarged.

The PM filter 26 is made of a porous material that traps particulatematter (PM) whose major component is soot in the exhaust gas. Similarlyto the NOx catalytic converter 25, the PM filter 26 contains anotherstorage reduction type NOx catalyst to reduce the NOx in the exhaustgases. The reaction catalyzed by the NOx catalyst burns (oxidizes) thetrapped particulate matter to remove them.

The oxidation catalytic converter 27 contains an oxidation catalyst. Theoxidation catalyst oxidizes hydrocarbons (HC) and carbon monoxides (CO)in the exhaust gas to purify the exhaust gas. The exhaust passage 14 hasan incoming gas temperature sensor 28 positioned upstream of the PMfilter 26 and an outgoing gas temperature sensor 29 positioneddownstream of the PM filter 26. The incoming gas temperature sensor 28detects the temperature of the incoming exhaust gas, which enters the PMfilter 26. The outgoing gas temperature sensor 29 detects thetemperature of the outgoing exhaust gas, which has passed through the PMfilter 26. A differential pressure sensor 30 is arranged to the exhaustpassage 14 to detect the differential pressure between a portion of theexhaust passage 14 positioned upstream of the PM filter 26 and a portionof the exhaust passage 14 positioned downstream of the PM filter 26. Anair-fuel ratio sensor 31 is disposed at a portion of the exhaust passage14 positioned upstream of the NOx catalytic converter 25 to detect anair-fuel ratio of the exhaust gases. Another air/fuel ratio sensor 32 isdisposed at a portion of the exhaust passage 14 positioned between thePM filter 26 and the oxidation catalytic converter 27 to detect theair-fuel ratio of the exhaust gases.

The engine 10 has an exhaust gas recirculation (EGR) system thatrecirculates a portion of the exhaust gas to the intake passage 12. TheEGR system includes an EGR passage 33 connecting the exhaust passage 14and the intake passage 12 to each other. The most upstream portion ofthe EGR passage 33 that is upstream is connected to the exhaust passage14. The EGR passage 33 has an EGR valve 36. The most downstream portionof the EGR passage 33 is connected to a portion of the intake passage 12positioned downstream of the intake throttle valve 19.

On the other hand, fuel injectors 40 are arranged at the combustionchambers 13 of the respective cylinders of the engine 10 to inject fuelfor combustion in the combustion chambers 13. The fuel injectors 40 ofthe respective cylinders are connected to a common rail 42 throughhigh-pressure fuel delivery pipes 41. A fuel pump 43 supplies highlypressurized fuel to the common rail 42. A rail pressure sensor 44attached to the common rail 42 detects the pressure of the highlypressurized fuel in the common rail 42. The fuel pump 43 also supplieslow pressurized fuel to a supplemental fuel valve 46 through a lowpressure fuel delivery pipe 45.

An electronic control unit (ECU) 50 executes various controls of theengine 10. The ECU 50 includes a CPU, ROM, RAM, input and output portsand so forth. The CPU executes various calculation processes forcontrolling the engine 10. The ROM stores programs and data necessaryfor the controls. The RAM temporarily stores the results of calculationsof the CPU, or the like. The input and output ports are used forinputting and outputting signals from and to external equipment,respectively.

The input ports of the ECU 50 are connected to, in addition to therespective sensors described above, an engine speedsensor 51 thatdetects the engine speed, an accelerator position sensor 52 that detectsthe operational amount of an accelerator, a throttle valve positionsensor 53 that detects the opening amount of the intake throttle valve19, an intake temperature sensor 54 that detects the intake temperatureof the engine 10, a coolant temperature sensor 55 that detects thetemperature of coolant of the engine 10, and so forth. The output portsof the ECU 50 are connected to drive circuits for the intake throttlevalve 19, the EGR valve 36, the fuel injectors 40, the fuel pump 43, thesupplemental fuel valve 46 and so forth.

The ECU 50 outputs command signals to the drive circuits of therespective devices connected to the output ports in response to engineoperational conditions grasped through detection signals input from therespective sensors. In this manner, the ECU 50 executes a control toopen the intake throttle valve 19, an EGR control based upon the controlof the opening of the EGR valve 36, controls of a fuel injection amount,a fuel injection time and a fuel injection pressure of each fuelinjector 40, a control of the fuel supplementation through thesupplemental fuel valve 46 and so forth.

In the embodiment constructed as described above, a filter regenerationis executed to prevent particulate matter from clogging the NOxcatalytic converter 25 and the PM filter 26. The filter regenerationincludes processes for burning the particulate matter that hasaccumulating in the exhaust system such as, for example, the NOxcatalytic converter 25 and the PM filter 26, to regenerate them. Inorder to make the regenerate the filter, the NOx catalytic converter 25and the PM filter 26 must be heated to a prescribed temperature. Thus,when the filter is regenerated, unburned fuel components are supplied tothe NOx catalytic converter 25 and the NOx catalyst of the PM filter 26.Thereby, a temperature increase control is executed to raise a catalystbed temperature to the temperature (for example, 600-700° C.) necessaryfor burning the particulate matter. The supplemental fuel valve 46supplies the unburned fuel components to the catalysts in thetemperature increase control.

In this connection, the temperature raising control for the filterregeneration in this embodiment starts when all of the followingconditions are satisfied.

It is the time that the filter regeneration is required. The requirementof the filter regeneration at this moment is made when the accumulationamount of the particulate matters in the exhaust system estimated fromthe engine operational condition reaches or exceeds a permissible amountand the clogged states of the filters including the PM filter 26 areverified.

The detection value of the entering gas temperature sensor 28 (enteringgas temperature thci) is equal to or higher than the lower limittemperature (for example, 150° C.) that allows the execution of thetemperature raising control. Also, the catalyst bed temperature of theNOx catalyst estimated from histories of the engine operationalconditions, the detection value of the entering gas temperature sensor28 and the detection value of the outgoing gas temperature sensor 29 isequal to or higher than the lower limit temperature that allows theexecution of the temperature raising control. To those lower limittemperatures, a lower limit value of the exhaust temperature and a lowerlimit value of the catalyst bed temperature are allotted, respectively.Both of the lower limit values of the temperatures can generate theoxidizing reaction that can raise the catalyst bed temperature.

The detection value of the entering gas temperature sensor 28 is lessthan the upper limit value C in a temperature range where excessivetemperature raising of the catalysts by heat generation accompanying thetemperature raising control can be avoided.

Similarly, the detection value of the outgoing gas temperature sensor 29is less than the upper limit value D in a temperature range where theexcessive temperature raising of the catalysts by the heat generationaccompanying the temperature raising control can be avoided.

The execution of the fuel supplementation to the exhaust gases ispermitted. In other words, it is under the engine operational conditionthat the fuel supplementation to the exhaust gases is permissible. Inconnection with this engine 10, the fuel supplementation to the exhaustgases is permitted under the condition that the engine is not stalling,cylinder discrimination has been finished and the output of the engine10 is not limited.

When the accumulated amount of the particulate matter decreases to apreset amount (for example, “0” ) by the execution of the filterregeneration through the temperature increase control, it is determinedthat the filter regeneration process is complete. The temperatureincrease control for the filter regeneration thus is terminated.

Next, with reference to the time chart of FIG. 2, an outline of thetemperature increase control will be described. The catalyst bedtemperature T under the temperature increase control increases relativeto the catalyst inlet port exhaust temperature Tb in accordance with theamount of the heat generated by the oxidizing reaction occurs whensupplemental fuel is supplied through the supplemental fuel valve 46.Under the temperature increase control, the target bed temperature Ttincreases incrementally, for example, 600, 630 and then 650. In order toraise the catalyst bed temperature T to the target bed temperature Tt,the supplemental fuel is supplied through the supplemental fuel valve 46to supply the unburned fuel components. However, occasionally, if theexhaust temperature of the engine 10 is low and the exhaust gas flowamount is low, the target bed temperature Tt is temporarily lowered sothat the fuel is not uselessly supplied through the supplemental fuelvalve 46. This is because, in such a state, the oxidizing reaction ofthe unburned fuel components does not proceed and the catalyst bedtemperature T cannot be raised even though the amount of fuel suppliedthrough the supplemental fuel valve 46 increases.

The the supply of fuel through the supplemental fuel valve 46 startswhen a supplement permission flag F1, shown in FIG. 2D, is set to “1”(time T1). The supplement permission flag F1 is then set to “0” afterbecoming “1.” When the fuel supplementation through the supplementalfuel valve 46 starts, the supplemental fuel is intermittently suppliedthrough the supplemental fuel valve 46 in accordance with supply pulsesshown in FIG. 2A. A supplemental time [a] of the fuel and a pause time[b] for the intermittent fuel supplementation are set based upon atemperature difference ΔTb between the target bed temperature Tt and thecatalyst inlet port exhaust temperature Tb, and a gas-flow amount Ga ofthe engine 10 (corresponding to the exhaust gas flow of the engine 10)detected by the airflow meter 16. As the inlet port exhaust temperatureTb, for example, a value estimated based upon the temperatures detectedby incoming exhaust gas temperature sensor 28 and the outgoing gastemperature sensor 29 are used. The intermittent fuel supplementationthat has started as described above continues until the fuelsupplementation is executed predetermined times. When the fuelsupplementation is executed such times, the fuel supplementation isterminated (time T2).

After the start of the fuel supplementation through the supplementalfuel valve 46, a heat generating fuel amount Q is calculated everypreset time. For example, a 16 ms heat generating fuel amount Q iscalculated every 16 ms. The amount Q is a fuel amount that is suppliedthrough the supplemental fuel valve 46 in the period of 16 ms. The 16 msheat generating fuel amount Q is summed up every time when it iscalculated based upon an equation “ΣQ←the last ΣQ+Q . . . (1)” tocalculate the total fuel supplementation amount ΣQ supplied through thesupplemental fuel valve 46 summed up from the fuel supplementation startmoment (T1), i.e., a heat generating fuel amount integration value ΣQindicative of the total fuel amount contributing to the heat generationby the oxidizing reaction. As indicated by the actual line of FIG. 2C,the heat generating fuel amount integration value ΣQ as thus calculatedrapidly increases during an supply period (A) which is a time periodbetween the start and end of the fuel supplementation. The heatgenerating fuel amount integration value ΣQ, however, is inhibited fromincreasing during a pause period of the fuel supplementation succeedingthe supply period (A).

In the meantime, after the start of the fuel supplementation through thesupplemental fuel valve 46, a 16 ms required fuel amount Qr iscalculated every preset time (16 ms). The 16 ms required fuel amount Qris an amount of the fuel that is required to be supplied through thesupplemental fuel valve 46 in 16 ms, i.e., a supply amount of the fuelnecessary for raising the catalyst bed temperature T to the target bedtemperature Tt. The 16 ms required fuel amount Qr is calculated usingthe temperature difference ΔTb between the target bed temperature Tt andthe catalyst inlet port exhaust temperature Tb, and the gas-flow amountGa of the engine 10. The lower the catalyst inlet port exhausttemperature Tb indicated by the actual line L2 of FIG. 2B relative tothe target bed temperature results in the larger the 16 ms required fuelamount Qr as thus calculated the 16 ms required fuel amount Qr is summedup every time when it is calculated based upon an equation “ΣQr←the lastΣQr+Qr . . . (2)” to calculate a required fuel amount integration valueΣQr indicative of an amount of the fuel from the fuel supplementationstart moment (T1) that is necessary to designate an average amount ofthe catalyst bed temperature T for the target bed temperature Tt. Asindicated by the dashed line of FIG. 2C, the required fuel amountintegration value ΣQr as thus calculated gradually increases incomparison with the increase of the heat generating fuel amountintegration value ΣQ (actual line).

When the required fuel amount integration value ΣQr reaches or exceedsthe heat generating fuel amount integration value ΣQ (time T3), thesupplement permission flag F1 changes to “1 (permission)” and theintermittent fuel supplementation through the supplemental fuel valve 46starts. On this occasion, the fuel amount corresponding to the heatgenerating fuel amount integration value ΣQ has been supplied throughthe supplemental fuel valve 46 after the time T1. The heat generatingfuel amount integration value ΣQ thus is subtracted from the requiredfuel amount integration value ΣQr. In addition, the heat generating fuelamount integration value ΣQ is cleared to be “0.” Following the start ofthe intermittent fuel supplementation through the supplemental fuelvalve 46, the supply period (A) starts again. When this supply period(A) ends, the pause period (B) starts. Therefore, the supply period (A)and the pause period (B) alternately repeat during the temperatureincrease control.

Additionally, the larger the catalyst inlet port exhaust temperature Tbleaves from the target bed temperature Tt on the decrement side of thistemperature Tt, the larger the calculated 16 ms required fuel amount Qrbecomes and the more rapidly the required fuel amount integration valueΣQr increases. As a result, the time necessary for the required fuelamount integration value ΣQr to reach or exceed the heat generating fuelamount integration value ΣQ becomes shorter, and the pause period (B)also becomes shorter. Meanwhile, the larger the catalyst inlet portexhaust temperature Tb approaches the target bed temperature Tt, thesmaller the calculated 16 ms required fuel amount Qr becomes and themore rapidly the required fuel amount integration value ΣQr increases.As a result, the time necessary for the required fuel amount integrationvalue ΣQr to reach or exceed the heat generating fuel amount integrationvalue ΣQ becomes longer, and the pause period (B) also becomes longer.

As thus described, the pause period (B) varies in response to thedeviated condition of the catalyst inlet port exhaust temperature Tbrelative to the target bed temperature Tt. Thereby, the average value ofthe fuel supplementation amount supplied through the supplemental fuelvalve 46 per unit time varies in response to the variation of the pauseperiod (B). The catalyst bed temperature T thus changes as, for example,indicated by the actual line L1 of FIG. 2B. A fluctuation center of thecatalyst bed temperature T which increases and decreases can becontrolled to be the target bed temperature Tt.

Next, with reference to flowcharts of FIGS. 3 and 4 showing a fuelsupplementation control routine, control processes for the fuelsupplementation through the supplemental fuel valve 46 under thetemperature increase control will be described. The ECU 50 executes thefuel supplementation control routine periodically, for example, byallowing the routine to cut in for a period (16 ms in this embodiment)every preset time.

In this routine, first, at step S101 of FIG. 3, the ECU 50 determineswhether the temperature increase control proceeds or not. If positivelydetermining, the ECU 50 goes to step 102 to calculate a 16 ms requiredfuel amount Qr based upon a temperature difference ΔTb appearing betweenthe target bed temperature Tt and the catalyst inlet port exhausttemperature Tb and the gas-flow amount Ga. At successive steps S103 andS104, the ECU 50 adjust the 16 ms required fuel amount Qr using alearned value K to remove the stationary difference between the catalystbed temperature T and the target bed temperature Tt.

More specifically, at step S103, the ECU 50 reads out the learned valueK stored in the nonvolatile RAM thereof. The learned value K has beencalculated through another routine to be a value corresponding to thestationary difference between the catalyst bed temperature T and thetarget bed temperature Tt and is stored in the nonvolatile RAM. Also, atstep S104, the ECU 50 sets the value obtained by multiplying the 16 msrequired fuel amount Qr by the learned value K as the new 16 ms requiredfuel amount Qr.

The ECU 50 sums up 16 ms required fuel amount Qr calculated at stepsS102 through steps S104 based upon the equation “ΣQr←the last ΣQr+Qr . .. (2)” at step S105. The required fuel amount integration value ΣQrdescribed above is obtained through the summing up calculation.Afterwards, the ECU 50 goes to step S106.

At step S106, the ECU 50 calculates a 16 ms heat generating fuel amountQ based upon an operational condition of the supplemental fuel valve 46.Next, the ECU 50 sums up the calculated 16 ms heat generating fuelamount Q based upon the equation “ΣQ←the last ΣQ+Q . . . (1)” at stepS107. The heat generating fuel amount integration value ΣQ describedabove is obtained through the summing up calculation.

At step S108, the ECU 50 determines whether the required fuel amountintegration value ΣQr reaches or exceeds the heat generating fuel amountintegration value ΣQ. If so, the ECU 50 proceeds to step S109 and setsthe supplement permission flag F1 to “1 (permission).” As a result, theECU 50 starts the intermittent fuel supplementation through thesupplemental fuel valve 46. Afterwards, at step S110, the ECU 50 sets avalue obtained through subtracting the heat generating fuel amountintegration value ΣQ from the required fuel amount integration value ΣQras the new required fuel amount integration value ΣQr. In addition, theECU 50, at step S111, clears the heat generating fuel amount integrationvalue ΣQ to be “0”.

Next, additionally referring to FIGS. 5 through 7, an outline ofcalculation processes for the learned value K that is used at step S103of FIG. 3 will be described.

FIG. 5 shows a condition under which the stationary difference appearsbetween the catalyst bed temperature T and the target bed temperature Ttduring the temperature increase control and the catalyst bed temperatureT (actual line) does not rise to the target bed temperature Tt (dashedline). Reasons why such a stationary difference appears are, forexample, that the fuel supplementation amount varies from its properamount due to occurrence of abnormality that the supplemental fuel valve46 is clogged, or that the gas-flow amount Ga varies from its properamount due to occurrence of abnormality of the airflow meter 16.

The calculated learned value K is corresponds to the difference betweenthe catalyst bed temperature T (catalyst bed temperature average valueTave) and the target bed temperature Tt and is used to adjust the 16 msrequired fuel amount Qr. When adjusting the 16 ms required fuel amountQr using the learned value K, the increase of the required fuel amountintegration value ΣQr is expedited or retarded, and the moment at whichthe required fuel amount integration value ΣQr reaches or exceeds theheat generating fuel amount integration value ΣQ varies. As a result,the pause periods (B) fluctuate and an average value of the fuel amountsupplied through the supplemental fuel valve 46 per unit time varies.Accordingly, the learned value K is reflected in the supply of theunburned fuel components to the catalysts.

In this connection, FIGS. 6 and 7 show variations appearing between asituation in which the learned value K corresponding to the differenceis reflected to the supply of the unburned fuel components to thecatalysts and another situation in which the learned value K is notreflected to the supply of the unburned fuel components to thecatalysts, under the condition that the stationary difference appearsbetween the catalyst bed temperature average value Tave and the targetbed temperature Tt as shown in FIG. 5.

The dashed line of FIG. 6 indicates a transition of the required fuelamount integration value ΣQr in the situation that the learned value Kis not reflected. In this situation, because the 16 ms required fuelamount Qr is not multiplied by the learned value K, the 16 ms requiredfuel amount Qr involves the difference to the proper value, resultedfrom the clogging of the supplemental fuel valve 46 and the abnormalityof the airflow meter 16. As a result, the required fuel amountintegration value ΣQr gradually increases in corresponding to thedifference to the 16 ms required fuel amount Qr. The moment at which therequired fuel amount integration value ΣQr reaches or exceeds the heatgenerating fuel amount integration value ΣQ is likely to delay.Therefore, the pause periods (B) become longer and the average value ofthe fuel amount supplied through the supplemental fuel valve 46 per unittime becomes smaller. The stationary difference shown in FIG. 5 thusappears between the catalyst bed temperature average value Tave and thetarget bed temperature Tt.

The dashed line of FIG. 7 shows a transition of the required fuel amountintegration value ΣQr in the situation that the learned value K isreflected. In this situation, because the 16 ms required fuel amount Qris multiplied by the learned value K, the 16 ms required fuel amount Qrdoes not involve any difference to the proper value, resulted from theclogging of the supplemental fuel valve 46 and the abnormality of theairflow meter 16. As a result, the required fuel amount integrationvalue ΣQr does not gradually increases but rapidly increases incorresponding to the difference to the 16 ms required fuel amount Qr.The moment at which the required fuel amount integration value ΣQrreaches or exceeds the heat generating fuel amount integration value ΣQis likely to come earlier. Therefore, the pause periods (B) becomeshorter and the average value of the fuel amount supplied through thesupplemental fuel valve 46 per unit time becomes larger. The stationarydifference thus disappears between the catalyst bed temperature averagevalue Tave and the target bed temperature Tt.

FIG. 8A is a time chart showing a transition manner of the learned valueK when the stationary difference disappears between the catalyst bedtemperature average value Tave and the target bed temperature Tt. Inthis regard, it is assumed that, as indicated by the dashed line and thechain line of FIG. 8, the stationary difference appears in such a mannerthat the catalyst bed temperature average value Tave is lower than thetarget bed temperature Tt.

The learned value K corresponding to such a difference is calculatedusing the 16 ms required fuel amount Qr (see FIG. 2C) and a 16 msestimation heat generating fuel amount Q′.

The 16 ms estimation heat generating fuel amount Q′ is calculated every16 ms. The 16 ms estimation heat generating fuel amount Q′ is anestimation value of the fuel amount supplied through the supplementalfuel valve 46 in 16 ms to obtain a rise amount ΔT′ of the catalyst bedtemperature T that rises from the catalyst inlet opening exhausttemperature Tb. In other words, the 16 ms estimation heat generatingfuel amount Q′ is an estimation value of the fuel amount thatcontributes to the heat generation made in 16 ms to obtain the riseamount ΔT′. The 16 ms estimation heat generating fuel amount Q′ iscalculated based upon the rise amount ΔT′ that is the differenceappearing between the catalyst bed temperature T and the catalyst inletport exhaust temperature Tb and the gas-flow amount Ga. The catalyst bedtemperature T can be, for example, a value estimated based upondetection amounts such as, for example, detection amounts of theentering gas temperature sensor 28 and the outgoing gas temperaturesensor 29. As described above, the 16 ms required fuel amount Qrrepresents a fuel amount that needs to be supplied through thesupplemental fuel valve 46 in 16 ms to raise the catalyst bedtemperature T to the target bed temperature Tt from the catalyst inletport exhaust temperature Tb, and the 16 ms required fuel amount Qr iscalculated based upon the temperature difference ΔTb appearing betweenthe target bed temperature Tt and the catalyst inlet port exhausttemperature Tb and the gas-flow amount Ga.

A ratio Qr/Q′ of the 16 ms required fuel amount Qr to the 16 msassumption heat generating fuel amount Q′ both described above is avalue corresponding to the difference of the catalyst bed temperature Trelative to the target bed temperature which is at the calculationmoment of the 16 ms required fuel amount Qr and the 16 ms assumptionheat generating fuel amount Q′. Therefore, an average value of the ratioQr/Q′ over a predetermined time period is calculated to obtain the valuecorresponding to the stationary difference of the catalyst bedtemperature average value Tave relative to the target bed temperatureTt. The average value of the ratio Qr/Q′ over the preset time period iscalculated as the learned value K. The learned value K is stored(updated) in the nonvolatile RAM when the target bed temperature Tt isstable at the value where the particulate matter is burned.

If the learned value K is updated at preset intervals, for example, atthe times T4, T5, T6 in FIGS. 8A and 8B in the processes describedabove, the learned value K stored in the nonvolatile RAM changes asshown in FIG. 8B and the pause periods (B) under the temperatureincrease control are gradually shortened. As a result, the average valueof the fuel amount supplied through the supplemental fuel valve 46increases, and the catalyst bed temperature average value Tave rises tothe target bed temperature Tt as shown in FIG. 8A. The stationarydifference between those temperatures disappears, accordingly.

Next, with reference to the flowchart of FIG. 9 showing a learned valuerenewing routine, the processes for the calculation and the renewal ofthe learned value K will be described in greater detail. The ECU 50executes the learned value renewing routine periodically, for example,by allowing the routine to cut in for a period (16 ms in thisembodiment) every preset time.

In this routine, first, the ECU 50 determines whether the calculation ofthe learned value K is permitted or not (S201). The calculation of thelearned value K is permitted when, for example, all of the followingconditions are satisfied for a certain long period.

It is under the temperature increase control.

The state in which the gas-flow amount Ga is few does not continue for along time such as, for example, 50 s.

It is not immediately after that the target bed temperature Tt haschanged to be higher than before.

It is not immediately after the renewal of the learned value K. In otherwards, it is not immediately after that the new learned value K has beenreflected to the fuel supplementation.

The target bed temperature Tt does not continuously decrease: Forexample, the decrease of the target bed temperature Tt does not continuemore than 15 s.

It is not in a prohibited period of the fuel supplementation through thesupplemental fuel valve 46. The fuel supplementation is prohibited when,for example, the catalyst bed temperature T excessively rises.

The entering gas temperature sensor 28 and the outgoing gas temperaturesensor 29 have no abnormality.

If negatively determining at step S201, the ECU 50 prohibits the learnedvalue K from being calculated (S206). If positively determining, the ECU50 calculates the ratio Qr/Q′ of the 16 ms required fuel amount Qr tothe 16 ms assumption heat generating fuel amount Q′ which are calculatedevery 16 ms, based upon those amounts. The ECU 50 then calculates theaverage value of the ratio Qr/Q′ over the preset time period to set thelearned value K (S202). If the calculation of the learned value Kcontinues more than the preset time period (S203: YES) and the targetbed temperature Tt is stable at a temperature (for example, 600° C.)which is equal to or larger than a temperature at which the particulatematter can be burned (S204: YES), the ECU 50 stores (renews) thecalculated learned value K to the nonvolatile RAM thereof. Thus, thelearned value K stored in the nonvolatile RAM is reflected to the fuelsupplementation through the supplemental fuel valve 46.

In the meantime, the learned value K is the value corresponding to thedifference between the catalyst bed temperature T (catalyst bedtemperature average value Tave) and the target bed temperature Tt. Thecatalyst bed temperature T is a parameter that changes in response tothe fuel supplementation through the supplemental fuel valve 46, and thetarget bed temperature Tt is a target value of the catalyst bedtemperature T. Therefore, the lower the catalyst bed temperature averagevalue Tave becomes than the target bed temperature Tt, the larger thelearned value K leaves from the value “1.0” on the increment side ofthis value. Meanwhile, the higher the catalyst bed temperature averagevalue Tave becomes than the target bed temperature Tt, the greater thelearned value K deviates from the value “1.0” to be lower than thisvalue.

On this occasion, if an abnormality occurs such that the catalyst bedtemperature average value Tave cannot be adjusted to the target bedtemperature during the temperature increase control, the learned value Kmay become excessively large or excessively small. For example, if thefuel supply system for the fuel supplementation is clogged, the supplyamount of the fuel supplied through the supplemental fuel valve 46 isreduced and which causes the catalyst bed temperature average value Taveto become lower than the target bed temperature Tt. The learned value Kmay exceed the value “1.0.” Thus, there abnormality can be determinedusing the changes of the learned value K accompanying the occurrence ofthe abnormality described above. More specifically, the idea is todetermine the abnormality based upon whether the learned value K iswithin a preset proper range, for example, in a range of “0.90 through1.4” or not when the learned value K is updated.

However, the abnormality that the catalyst bed temperature Tave cannotbe adjusted to the target bed temperature Tt does not necessarilypermanently occur but may only be temporary.

In this connection, if deposits adhere to the periphery of a nozzle ofthe supplemental fuel valve 46 because of the use of poor quality fuel,the fuel amount supplied through the supplemental fuel valve 46 is lessthan the proper amount, and the catalyst bed temperature average valueTave is below the target bed temperature Tt. Accordingly, theabnormality may occur such that the catalyst bed temperature averagevalue Tave cannot be adjusted to the target bed temperature Tt. In thissituation, however, the deposits may occasionally depart from the nozzleperiphery when the supplemental fuel is supplied through thesupplemental fuel valve 46. Accordingly, even though the aboveabnormality occurs, it may only be temporary.

Also, in another situation such that the gas-flow amount Ga detected bythe airflow meter 16 differs from an actual gas-flow amount because ofadhesion of foreign substances to a detecting portion of the airflowmeter 16, as a result the 16 ms required fuel amount Qr calculated basedupon the gas-flow amount Ga may be larger than a proper amount. If the16 ms required fuel amount Qr is larger than the proper amount, thepause periods B under the temperature increase control are shortened.The catalyst bed temperature average value Tave thus exceeds the targetbed temperature Tt, and the abnormality occurs where the catalyst bedtemperature average value Tave cannot be adjusted to the target bedtemperature Tt. In this situation, however, the foreign substancesadhering to the detecting portion of the airflow meter 16 mayoccasionally depart from the periphery of the detecting portion in theprocess that the air flows around the detecting portion. Accordingly,even though the above abnormality occurs, it may only be temporary.

If the abnormality is immediately determined, without considering theabove situations, when the learned value K falls outside of the properrange even once when the learned value K is updated (time T7 of FIG.10), the abnormality determination would be incorrect if the abnormalityis temporary and thus disappears later and the learned value K returnsto a value within the proper range when the learned value K issubsequently updated again (time T8).

In this embodiment, therefore, the ECU 50 determines whether the learnedvalue K is out of the proper range or each time the learned value K isupdated. If the learned value K falls outside of the proper range, theECU 50 increases a count value of a counter C by “1.” If the learnedvalue K is in the proper range, the ECU 50 resets the count value of acounter C to an initial value “0.” FIGS. 11A and 11B show thetransitions of the learned value K over several updates and thetransitions of the number of counts by the counter C accompanying thetransitions of the learning value K, respectively. In the counter C, theinitial count value is set to be “0,” and the count value increases by“1” from the initial value “0.” When the count value of the counter Cexceeds a determination value, which is equal to or greater than “2”(time T10) it is determined that the learned value K has fallen outsideof the proper range over several updates (three times in thisembodiment) of the learned value K, the ECU 50 determines that anabnormality is present.

In this connection, when the abnormality disappears before the countvalue of the counter C reaches or exceeds the determination value and,as indicated by the chain double-dashed line of FIG. 11A, the learnedvalue K returns to a value within the proper range (time 9).Accordingly, the count value is reset to the initial value “0” asindicated by the chain double-dashed line of FIG. 11B. It is determinedthat an abnormality is not present. That is, even though the learnedvalue K falls outside of the proper range, it is determined that anabnormality is not present unless the learned value K continues to falloutside of the proper range over three successive updates of the learnedvalue. Therefore, when the abnormality temporarily occurs such that thecatalyst bed temperature average value Tave cannot be adjusted to thetarget bed temperature Tt, an incorrect determination that anabnormality is present will not be made.

Next, with reference to the flowchart of FIG. 12 showing an abnormalitydiagnosing routine, the processes for determining the abnormality willbe described. The ECU 50 executes the abnormality diagnosing routineperiodically, for example, by allowing the routine to cut in for aperiod (16 ms in this embodiment) at predetermined intervals.

In this routine, the ECU 50 executes processes (steps S303 through S305)for changing the count value of the counter C based upon a magnitude ofthe learned value K while the temperature increase control beingexecuted (S301: YES) and the learned value K is updated at this moment(S302: YES). More specifically, first, the ECU 50 determines whether thelearned value K is out of the proper range or not (S303). If thedetermination is positive, the ECU 50 increases the count value of thecounter C by “1” (S304). If negatively determining, the ECU 50 resetsthe count value to the initial value “0” (S305). The ECU 50 stores thecount value of the counter C into the nonvolatile RAM thereof everyrenewal of the learned value K. When the engine 10 starts next time, theECU 50 sets the initial value to be the value stored in the nonvolatileRAM.

Successively, the ECU 50 determines whether the count value of thecounter C reaches or exceeds the determination value (“3” in thisembodiment) (S306). If positively determining, the ECU 50 determines theabnormality and stores “1 (abnormal)” as a value of an abnormality flagF2 into an allotted area of the nonvolatile RAM (S307). In addition, theECU 50 turns a warning lamp on which is placed at a location around adriver's seat or the like of the automobile that has the engine 10(S308) to warn the driver that an abnormality has occurred.

Meanwhile, if negatively determining, the ECU 50 further determineswhether the filter regeneration has not been completed yet or not(S309). If negatively determining at step S309 (filter regeneration hasbeen completed), the ECU 50 resets the count value of the counter C tothe initial value “0” (S310). On this occasion, even though, as shown inFIG. 13A, the learned value K is out of the proper range due to theabnormality at the renewal moment, the filter regeneration can becompleted before the count value of the counter C reaches thedetermination value (“3”), for example, when the count value reaches “2”as shown in FIG. 13B, under a condition that the abnormality does notaffect the filter regeneration so much (time T11). In such a situation,the ECU 50 resets the count value of the counter C to the initial value“0.”

If the ECU 50 positively determines that the filter regeneration has notbeen completed yet at step S309 of FIG. 12, the ECU 50 then determineswhether the time that has elapsed since the start of the filterregeneration is equal to or exceeds a permissible time period (forexample, one hour) (S311). If positively determining at step S311, theECU 50 further determines that an abnormality is present and executessteps S307, S308 in turn. On this occasion, if the learned value K, asshown in FIG. 14A, is updated to a value that falls outside of theproper range due to the abnormality, the learned value K may be againupdated to a value that falls outside of the proper range later. Unless,however, the target bed temperature Tt stably maintains a catalyst bedtemperature above the temperature at which the particulate matter burns,the learned value K is not actually updated to such a value fallingoutside of the proper range. Because the particulate matter are hardlyburned in the filter regeneration under the condition, the amount of theaccumulated particulate matter does not decrease to “0.” Thus, thefilter regeneration thus is hardly completed. As a result, as shown inFIG. 14B, the time that has elapsed since the filter regeneration startsreaches or exceeds the permissible time period without the count valueof the counter C reaching the determination value (time T12). Based uponthis situation, the ECU 50 determines the abnormality and stores “1(abnormal)” as the value of the abnormality flag F2 into the nonvolatileRAM and turns the warning lamp on.

According to the embodiment as described in detail, the followingeffects can be obtained.

(1) Under the temperature increase control for the filter regeneration,the abnormality can occur such that the catalyst bed temperature averagevalue Tave cannot be adjusted to the target bed temperature Tt. However,such abnormality does not necessarily permanently occur but cantemporarily occur. On this occasion, if the abnormality is immediatelydetermined when the learned value K becomes out of the proper range evenonce at a renewal moment, the abnormality determination is incorrectunder the condition that the abnormality is temporary and thusdisappears later and the learned value K returns to a value within theproper range at a later renewal moment. In this embodiment, however, theabnormality is determined only when the determination that the learnedvalue K at the renewal time becomes out of the proper range is madeevery renewal successively three times. More specifically, if thelearned value K at the renewal time is out of the proper range, thecount value of the counter C is increased. The count value is reset tothe initial value “0” if the learned value K is in the proper range.When the count value reaches the determination value (“3” in thisembodiment), the abnormality is determined. Therefore, if theabnormality temporarily occurs such that the catalyst bed temperatureaverage value Tave cannot be adjusted to the target bed temperature Tt,the abnormality is not incorrectly determined.

(2) The learned value K necessary for determining the abnormality isupdated during the temperature increase control for the filterregeneration. The filter regeneration is regularly executed every timewhen the accumulation amount of the particulate matter reaches orexceeds the permissible amount accompanying the operation of the engine10. Because the learned value K is updated whenever the temperatureincrease control for the filter regeneration is regularly made, theabnormality can be determined together with the renewal of the learnedvalue K. Chances for the abnormality determination can be keptsufficiently.

(3) If the abnormality temporarily occurs such that the catalyst bedtemperature average value Tave does not reach the target bed temperatureTt during the temperature increase control for the filter regeneration,the updated learned value K is out of the proper range and the countvalue of the counter C is increased. However, if the temporaryabnormality does not affect the filter regeneration, the filterregeneration can be occasionally completed because the accumulationamount of the particulate matter becomes “0” before the count valuereaches or exceeds the determination value. On this occasion, if thecount value is kept to be a value larger than “0” (for example, “2”),the count value early reaches or exceeds the determination value whenthe learned value K becomes out of the proper range because thetemporary abnormality occurs again during the temperature increasecontrol for the filter regeneration in the next time. The abnormalitythus can be incorrectly determined. In this embodiment, however, thecount value of the counter C is reset to the initial value “0” wheneverthe filter regeneration is completed. The abnormality determinationdescribed above can be avoided, accordingly.

(4) During the temperature increase control to regenerate the filter,the learned value K can be updated to a value out of the proper rangewhen the abnormality temporarily occurs such that the catalyst bedtemperature average value Tave does not reach the target bedtemperature. Even though there can be such a chance of the renewal, thelearned value K is not updated to be the value out of the proper rangeunless the target bed temperature Tt is stable at a value which islarger than the value at which the particulate matter can be burned.Under the condition, despite of the occurrence of the abnormality, thefilter regeneration is continued without the count value of the counterC reaching or exceeding the determination value, i.e., without theabnormality being determined. In the filter regeneration under thecondition, the accumulating particulate matter are hardly burned and theaccumulation amount of the particulate matter does not decrease to “0.”The filter regeneration thus is hardly completed. In this embodiment,however, the abnormality is determined even though the count value ofthe counter C does not reach the determination value, if the filterregeneration is not completed although the time elapsing from the startmoment of the filter regeneration reaches or exceeds the permissibletime period. Therefore, the abnormality is determined whenever theabnormality actually occurs.

(5) The count value of the counter C is stored in the nonvolatile RAM ofthe ECU 50. The count value stored in the nonvolatile RAM is set to bethe initial value when the engine 10 starts next time. Assuming that thecount value of the counter C is reset to the initial value “0” everystop of the engine 10, the chances for determining the abnormality candecrease under a condition that the engine 10 frequently repeats stopand start. The abnormality thus is not able to be determined even thoughthe abnormality actually occurs. In addition, accompanying the delay ofthe abnormality determination, the filter regeneration is not madeproperly due to the abnormality and the particulate matter canexcessively accumulate. Consequently, the PM filter or relating partscan need to be exchanged. In the embodiment, however, the above problemsare resolved through the treatment of the count value of the counter Cprovided at the start moment of the engine 10.

The embodiment described above can be modified, for example, as follows.

In the above embodiment, the abnormality is determined regardless of thecount value of the counter C when the time elapsing from the startmoment of the filter regeneration reaches or exceeds the permissibletime period. However, this determination of the abnormality is notnecessarily made.

The count value of the counter C is reset to the initial value “0” atthe completion of the filter regeneration. This reset, however, is notnecessarily made.

In an engine such that the temperature increase control is executed bythe fuel supplementation through the supplemental fuel valve 46, themost possible causes for occurrence of the temporary abnormality isspeculated to be the temporary adhesion of the deposits to thesupplemental fuel valve 46. In consideration of the speculation, thecount value of the counter C can be increased only when the learnedvalue K at the renewal time becomes out of the proper range on theincrement side.

In an internal combustion engine having a NOx catalyst, sulfur poisoningrecovery is made to release a sulfur component occluded in the NOxcatalyst. The temperature increase control is applied for the Sulfurpoisoning recovery. The abnormality can be determined during thetemperature increase control for the sulfur poisoning recovery.

As the determination value used for determining the abnormality, thevalue “2” or integers equal to or larger than “4” can replace the value“3” used in the above embodiment.

The unburned fuel components can be supplied to the exhaust system by anauxiliary injection (after-injection) made in exhaust strokes andexpansion strokes after the fuel for combustion in the combustionchambers is injected through the fuel injector 40. In this connection,the supplemental fuel valve 46 can be omitted.

While the invention has been described with reference to exampleembodiments thereof, it is to be understood that the invention is notlimited to the described embodiments or constructions. To the contrary,the invention is intended to cover various modifications and equivalentarrangements. In addition, while the various elements of the embodimentsare shown in various example combinations and configurations, othercombinations and configurations, including more, less or only a singleelement, are also within the scope of the invention.

1. An abnormality diagnosing device for an internal combustion enginecomprising: a temperature increase control section for executing atemperature increase control for increasing a temperature of a catalystdisposed in an exhaust system to a target bed temperature by supplyingan unburned fuel component to the catalyst; an updating section forexecuting updating of a learned value based upon a catalyst bedtemperature under the temperature increase control by the temperatureincrease control section and the target bed temperature so that thelearned value corresponds to a difference between the respectivetemperatures; a learned value determining section for determiningwhether the learned value is outside of a proper range or not when thelearned value is updated; and an abnormality determining section fordetermining that an abnormality is present only when the learned valuedetermining section determines that the learned value falls outside ofthe proper range over several successive updates of the learned value.2. The abnormality diagnosing device for an internal combustion engineaccording to claim 1, wherein the internal combustion engine has asupplemental fuel valve for supplying supplemental fuel upstream of thecatalyst in the exhaust system.
 3. The abnormality diagnosing device foran internal combustion engine according to claim 1, wherein the exhaustsystem of the internal combustion engine has a filter for trappingparticulate matter, the temperature increase control for increasing thetemperature of the catalyst to the target bed temperature is executed bysupplying the unburned fuel component to the catalyst when to burn theparticulate matter to regenerate the filter so that an accumulationamount of the particulate matter trapped in the filter is to less than aprescribed amount.
 4. The abnormality diagnosing device for an internalcombustion engine according to claim 1, further comprising: a countingsection for increasing a count value when the learned value determiningsection determines that the learned value has fallen outside of theproper range and for resetting the count value to an initial value whenthe learned value determining section determines that the learned valueis in the proper range, wherein the abnormality determining sectiondetermines that the abnormality is present when the count value is equalto or greater than a determination value that is equal to or greaterthan a value that is incremented at least twice from the initial value,and the counting section resets the count value to the initial valuewhen the filter regeneration is completed.
 5. The abnormality diagnosingdevice for an internal combustion engine according to claim 1, furthercomprising: a counting section for increasing a count value when thelearned value determining section determines that the learned value hasfallen outside of the proper range and for resetting the count value toan initial value when the learned value determining section determinesthat the learned value is in the proper range, wherein the learned valueis updated when the catalyst bed stably maintains a catalyst bedtemperature that is equal to or higher than the temperature at which theparticulate matter is capable of being burned, and the abnormalitydetermining section determines that the abnormality is present when thecount value given by the counting section is equal to or greater than adetermination value that is equal to or greater than a value that isincremented at least twice from the initial value, and determines theabnormality regardless of the count value if the filter regeneration isnot completed after the elapsed time from when the filter regenerationstarts reaches or exceeds a permissible time period.
 6. The abnormalitydiagnosing device for an internal combustion engine according to claim4, wherein the counting section increases “1” per once, the initialvalue is “0,” and the determination value is an integer which is equalto or greater than “2”.
 7. The abnormality diagnosing device for aninternal combustion engine according to claim 1, wherein the abnormalitydetermining section determines that the abnormality is present when thelearned value determining section determines that the learned valuevaries to be larger than the proper range over several successiveupdates of the learned value.
 8. The abnormality diagnosing device foran internal combustion engine according to claim 1, wherein the unburnedfuel component is supplied to the catalyst by an auxiliary injectionmade in an exhaust stroke or an expansion stroke after fuel injected forcombustion in a combustion chamber from a fuel injector.
 9. Anabnormality diagnosing method for an internal combustion enginecomprising: executing a temperature increase control for increasing atemperature of a catalyst disposed in an exhaust system to a target bedtemperature by supplying an unburned fuel component to the catalyst;executing updating a learned value based upon a catalyst bed temperatureunder the temperature increase control and the target bed temperature sothat the learned value corresponds to a difference between therespective temperatures; determining whether the learned value fallsoutside of a proper range or not every time the learned value isupdated; and determining abnormality when it is determined that thelearned value falls outside of the proper range over several successiveupdates of the learned value.
 10. The abnormality diagnosing method foran internal combustion engine according to claim 9, wherein the exhaustsystem of the internal combustion engine has a filter for trappingparticulate matter, the temperature increase control for increasing thetemperature of the catalyst to the target bed temperature is executed bysupplying the unburned fuel component to the catalyst when a filterregeneration is made to burn the particulate matter so that anaccumulation amount of the particulate matter trapped by the filter isto be less than a preset amount.
 11. The abnormality diagnosing methodfor an internal combustion engine according to claim 9, furthercomprising: increasing a count value when the learned value isdetermined to fall outside of the proper range, and resetting the countvalue to an initial value when the learned value is determined to be inthe proper range, wherein an abnormality is determined to be presentwhen the count value is equal to or greater than a determination valuewhich that is equal to or greater than a value that is incremented atleast twice from the initial value, and the count value is reset to theinitial value when the filter regeneration is completed.
 12. Theabnormality diagnosing method for an internal combustion engineaccording to claim 9, further comprising: increasing a count value whenthe learned value is determined to be outside the proper range andresetting the count value to an initial value when the learned value isdetermined to be in the proper range, wherein the learned value isupdated when the catalyst bed temperature is stably maintained at atemperature that is equal to or above the temperature at which theparticulate matter is capable of being burned, and the abnormality isdetermined to be present when the count value is equal to or greaterthan a determination value that is equal to or greater than a value thatis incremented at least twice from the initial value, and theabnormality is determined to be present regardless of the count value ifthe filter regeneration is not completed a time period has elapsed froma start moment of the filter regeneration reaches or exceeds apermissible time period.